The field of the invention is the separation of hydrogen halide gases and the present invention is particularly concerned with the separation of hydrogen chloride from a mixture of hydrogen chloride contaminated with hydrogen bromide.
Hydrogen chloride is frequently obtained in industrial processes contaminated with hydrogen bromide, for example, in the case of the chlorination of bromine-containing substances or in the case of reactions with bromine chloride or bromine/chlorine mixtures.
Hydrogen chloride, which is produced from chlorine and hydrogen or obtained as a by-product from the chlorination of hydrocarbons, contains hydrogen bromide in the order of magnitude of 50 to 100 ppm. The source of these impurities is the bromine unavoidably obtained from the bromides contained in the sols employed when chlorine is obtained electrolytically.
A hydrogen bromide content always has an adverse effect during the further processing of hydrogen chloride obtained in this way, since, on the one hand, it lowers the yield of the desired product and, on the other hand, makes a purification operation necessary. Thus, for example, vinyl chloride, which is prepared from acetylene and hydrogen chloride, must be freed from proportions of vinyl bromide by distillation in order to obtain a flawless material for the polymerization to polyvinyl chloride. In addition to the necessity of a special purificiation stage, the highly corrosive character of hydrogen bromide makes its presence in hydrogen chloride appear extremely undesirable. Even traces of moisture make hydrogen bromide containing gas mixtures highly aggressive towards many metallic materials which are used industrially.
A process for the removal of hydrogen bromide from hydrogen chloride is known from Israeli Patent Specification 34,481 and as reported in Chemical Abstracts, Vol. 80 (1974) 16843q. It is characterized in that the hydrogen bromide is converted (oxidized) to bromine with the aid of chlorine and the bromine is removed with the excess chlorine in a subsequent reaction. However, this process was developed for the hydrolysis of magnesium salts and because of the very specific process conditions does not offer a generally usable method for separating hydrogen chloride and hydrogen bromide or for separating hydrogen bromide off from hydrogen chloride.
The physical properties and methods of preparation of hydrogen bromide and sodium bromide, prepared by the neutralization of sodium carbonate or hydroxide with hydrobromic acid, are disclosed in the Kirk-Othmer, "Encyclopedia of Chemical Technology," 2nd edition, vol. 3 (1964) pp. 767 and 768 and vol. 18 (1969) pp. 484 and 485.
The state of the art of the manufacture and processing of hydrochloric acid may be ascertained by reference to the Kirk-Othmer "Encyclopedia of Chemical Technology" 2nd ed., vol. 11 (1967) pp. 307-337, particularly pp. 314-315 where it is disclosed that 75% of U.S. hydrochloric acid production for the years 1961-66 came from chlorination processes, and pp. 315-323 under the section Gas Treatment and U.S. Pat. No. 4,115,530, the disclosures of which are incorporated herein.
The disclosure of U.S. patent application Ser. No. 10,048, which is not a part of the state of the art, is an improvement over U.S. Pat. No. 4,115,530.